I made the switch a couple years ago and like RunSignUp a lot better. One of the major differences is the reporting options available in RSU. If you want a snapshot of current financials, registrants, t-shirt distribution, city representation, etc it is extremely easy with RSU. It is constantly evolving with new features monthly.
They also allow the RD to decide if people can defer or transfer their registration or switch distances without the RD having to get involved. The saves a lot of time for larger event.
Random cool stuff you didnt know you needed...
If you use RSU results you can set up custom finishers certificates
Shirt Projection Tool (helps you decide how many to order.)
RSU does not offer any marketing like active. We did active instant ads last year for one of our events and undecided if we will next year (we had registrations available on both sites but pushed our main reg RSU..had about 3500 on RSU and 350 on active.)
We felt we had a better roi with facebook ads. RunSignUp has conversion code tracking for facebook and google so you can track how many actual registrations came from those ads. When the participant finalizes their registration the conversion code is triggered.